How come i'm feeling so bad?

i'm a 21 year old female who hasn't gotten very sick in awhile. i've was feeling fine earlier today, studying for a chemistry test and got really sleepy. i took about a 45 minute nap and when i woke up i felt pretty well rested. when i got up and went to the kitchen, however, i felt really sluggish. i felt a quick wave of naseua (just a real "blah" feeling) and felt as if i would faint if i continued to stand, so i layed back down on the bed. after a couple of minutes i tried to get back up (slowly) and walk to the bathroom but the same feeling came over me. i'm studying to be a nutritionist so i can't help but feel maybe my body is just low on some sort of mineral or vitiamin. it's exam time and i've been really stressed and have been eating horribly aka french fries and chicken strips. :-( also if it would help anyone figure out maybe what my body is trying to tell me it's about 2 days away from "that time of the month" :-(